Columns or other memory units within a memory device may include defects that prevent data from being accurately written or read. Defects may occur during manufacturing of memory chips or dies, or may arise over time as memory is used. Bad or defective columns or other memory units may be skipped when reading and writing data. However, defects in the skipping mechanism may cause a memory controller to write to or read from a column that has been marked for skipping. Inconsistent skipping can cause data errors.